net: Introduce unregister_netdevice_many()

Introduce rollback_registered_many() and unregister_netdevice_many()

rollback_registered_many() is able to perform necessary steps at device dismantle
time, factorizing two expensive synchronize_net() calls.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1119,6 +1119,7 @@ extern int		dev_queue_xmit(struct sk_buff *skb);
 extern int		register_netdevice(struct net_device *dev);
 extern void		unregister_netdevice_queue(struct net_device *dev,
 						   struct list_head *head);
+extern void		unregister_netdevice_many(struct list_head *head);
 static inline void unregister_netdevice(struct net_device *dev)
 {
 	unregister_netdevice_queue(dev, NULL);

net/core/dev.c

@@ -4637,14 +4637,19 @@ static void net_set_todo(struct net_device *dev)
 	list_add_tail(&dev->todo_list, &net_todo_list);
 }
 
-static void rollback_registered(struct net_device *dev)
+static void rollback_registered_many(struct list_head *head)
 {
+	struct net_device *dev;
+
 	BUG_ON(dev_boot_phase);
 	ASSERT_RTNL();
 
-	/* Some devices call without registering for initialization unwind. */
+	list_for_each_entry(dev, head, unreg_list) {
+		/* Some devices call without registering
+		 * for initialization unwind.
+		 */
 		if (dev->reg_state == NETREG_UNINITIALIZED) {
-		printk(KERN_DEBUG "unregister_netdevice: device %s/%p never "
+			pr_debug("unregister_netdevice: device %s/%p never "
 				 "was registered\n", dev->name, dev);
 
 			WARN_ON(1);
@@ -4660,9 +4665,11 @@ static void rollback_registered(struct net_device *dev)
 		unlist_netdevice(dev);
 
 		dev->reg_state = NETREG_UNREGISTERING;
+	}
 
 	synchronize_net();
 
+	list_for_each_entry(dev, head, unreg_list) {
 		/* Shutdown queueing discipline. */
 		dev_shutdown(dev);
 
@@ -4686,12 +4693,22 @@ static void rollback_registered(struct net_device *dev)
 
 		/* Remove entries from kobject tree */
 		netdev_unregister_kobject(dev);
+	}
 
 	synchronize_net();
 
+	list_for_each_entry(dev, head, unreg_list)
 		dev_put(dev);
 }
 
+static void rollback_registered(struct net_device *dev)
+{
+	LIST_HEAD(single);
+
+	list_add(&dev->unreg_list, &single);
+	rollback_registered_many(&single);
+}
+
 static void __netdev_init_queue_locks_one(struct net_device *dev,
 					  struct netdev_queue *dev_queue,
 					  void *_unused)
@@ -5271,6 +5288,22 @@ void unregister_netdevice_queue(struct net_device *dev, struct list_head *head)
 }
 EXPORT_SYMBOL(unregister_netdevice_queue);
 
+/**
+ *	unregister_netdevice_many - unregister many devices
+ *	@head: list of devices
+ *
+ */
+void unregister_netdevice_many(struct list_head *head)
+{
+	struct net_device *dev;
+
+	if (!list_empty(head)) {
+		rollback_registered_many(head);
+		list_for_each_entry(dev, head, unreg_list)
+			net_set_todo(dev);
+	}
+}
+
 /**
  *	unregister_netdev - remove device from the kernel
  *	@dev: device